The present invention relates generally to the field of telecommunications and, in particular, to transport of digitized signals over a ring network such as the transport of digitally encoded video and/or audio signals for video on demand, near video on demand, video conferencing, distance learning, other multi-party video services and voice over IP.
Telecommunications companies, such as cable television operators, provide xe2x80x9cprogramingxe2x80x9d or xe2x80x9ccontentxe2x80x9d to subscribers over a wide variety of networks. Initially, cable operators provided subscribers with improved access to a number of commercial and premium programming stations over networks of coaxial cables. Further, new commercial programming stations have entered the marketplace over the cable networks. These stations include the USA Network, Nickelodeon, CNN, and others.
To further increase revenues, some cable operators further provide access to selected movies and other programming on a pay-per-view basis. Conventionally, the cable operators schedule a number of showings of specified movies on selected channels and at specified times. Subscribers can view these programs by contacting the cable company and paying a fee for the show. Typically, these systems operate by scrambling the video portion of the pay per view channel. When a subscriber requests the program, the cable operator activates the descrambler at the subscriber""s premises to descramble the selected show at the scheduled time.
With the increase in competition for the entertainment resources of consumers, cable operators and other content providers have tried to create more flexible systems for delivering video programming to subscribers. For example, the cable industry has begun to design networks that provide xe2x80x9cvideo on demand.xe2x80x9d Essentially, with this type of system, a user can select from a list of movies for viewing at any time. Many of these designs depend on using digitized compressed video on a video server with random access storage. One problem with delivering video on demand is the cost of developing a robust enough backbone network with sufficient capacity to carry the video traffic.
Cable operators looking to further increase revenues are attempting to develop other services such as: video conferencing, distance learning systems and packetized voice telephony service over their networks. This latter system is commonly referred to as xe2x80x9cvoice over IPxe2x80x9d telephony.
Synchronized Optical Networks (SONET) rings are a conventional high capacity backbone network. SONET rings were developed around the ability to transport low bandwidth (64 kbps) voice channels in a high speed ring network for telephony service. SONET rings are expensive and cumbersome when handling high bandwidth signals commonly associated with the transport of video signals or the variable sized packets that would be used in systems that were meant to carry packetized video as well as packetized Voice over IP, and other digitized services, on the same network. This is, in part, due to the fact that SONET equipment typically works with fixed sized channels of 64 kbps and therefore usually requires small fixed sized data packets, e.g., asynchronous transfer mode (ATM) cells, which can be small in comparison to data packets containing video data and cumbersome in handling variable length data.
The network operators are desirous of providing these services over an industry standards based cable plant, such as Hybrid Fiber Coax (HFC) using Cable labs Docsis MCNS cable data modems, or copper wire using Digital Subscriber Loop (DSL) modems. Virtually all of these standards are based on packetized data standards such as Ethernet. The use of SONET further complicates the implementation of these systems by often requiring the conversion, at great expense, of Ethernet packets to ATM cells for backbone transport.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a network that allows the efficient transport of high bandwidth digital data, e.g., video and/or audio signals, in a ring network.
The above mentioned problems with telecommunications systems and other problems are addressed by the present invention and will be understood by reading and studying the following specification. A telecommunications network is described which uses a ring of switches to provide a backbone transport mechanism for data packets that is transparent to the data and protocols contained in the data packets. The ring switches can include a number of different features, alone or in combination, to implement this backbone network. Ring switches with such features are described in detail in die ""919 Application and application Ser. No. 09/137,669, entitled Telecommunication Network with Variable Address Learning, Switching and Routing, and include, but are not limited to the following:
1. A ring switch in which packets are switched on to unidirectional ring on comparing a destination identifier, which may already be in the packet, to a table in the ring switch.
2. A ring switch in which packets are switched off and removed from the unidirectional ring based on comparing a destination identifier, which may already be in the packet, to a table in the ring switch thus freeing bandwidth for use by other devices and switches on the ring.
3. A ring switch in which packets received from a unidirectional ring, are placed back on the unidirectional ring based on comparing a destination identifier, which may already be in the packet, to a table in the ring switch.
4. A ring switch in which packets which have traveled completely around the ring are terminated by comparing a source identifier which may be already in the packet to a table, a switch identifier that was added by the ring switch to a table, or a hop counter that has reached a threshold value.
5. A ring switch in which no modification is made to the original packet in order to cause the packet to transmit from the local ports of one ring switch, around the ring to the local ports of another ring switch because the destination identifiers used to compare to the table are already contained in the original packet.
6. A ring switch in which no modification is made to the original packet in order to cause the packet to be terminated when the packet has traveled completely around the ring because the source identifiers used to compare to the table are already contained in the original packet.
7. A ring switch in which the tables are built automatically (self learned) by virtue of reading the source identifiers of each packet received by the ring switch.
8. A ring switch in which the original packet is modified slightly by the ring switch when placing the packet on a unidirectional ring by the addition of a switch identifier such that when the packet has traveled completely around the ring and back to the originating ring switch, the packet is terminated by detecting its own switch identifier.
9. A ring switch in which the original packet is modified slightly by the ring switch when placing the packet on the unidirectional ring by the addition of a counter, such that when the packet passes through each ring switch, the counter is incremented (or decremented) and the packet is terminated by any switch when the counter reaches a selected value.
This transport mechanism is simple and low cost to implement. Such networks can carry, for example, video signals among primary and secondary sites such as a head end or central office and hubs of a cable network or DSL network to provide video on demand, near video on demand, video conferencing, distance learning and other video based services. Such networks can also provide telephony service such as voice over IP.